Why does a timer base fail????

[metriccrescentwrench]

This is the 1990 Johnson 200 I bought on ebay, and really thought I had the last of the problems taken care of. I had done the tests on the electrical system as called for in the factory manual, and they pointed to a bad timer base. I found a timer base off a 1996 Johnson 225 which was being parted out due to a cracked block, installed it, and the engine idled fantastic on muffs, better than it ever had before. When I took the boat for a test drive it ran great, I couldn't have been happier.

Fast forward to today. I just got back from the lake and it's running EXACTLY like it did before I replaced the timer base. Idles poorly, I have to give it throttle just to keep it idling, and there's an intermittent miss at idle and no-wake speed where it will die if I don't immediately feed it some throttle. It was also about 5 mph off on the top end as compared to the previous time out as well.

I haven't repeated the tests on the electrical system yet - I'm too at the moment to mess with it. But if in fact that timer base I installed failed so fast - why? What makes them go bad? Could a problem with the rectifier/regulator kill a timer base? I don't believe I have a bad regulator/rectifier because it's charging (about 14.8 V at speed) and the tach works properly, but I haven't done any testing on that so I can't say for sure that it doesn't have a problem.

Anyone?

thanks

 

[boobie]

Re: Why does a timer base fail????

Have you got the proper test equipment and OEM factory service manual to check this mtr out? You may have something else wrong with it other than the timer base. Or else the used one you got was bad also.

 

[metriccrescentwrench]

Re: Why does a timer base fail????

Yes I've got the factory service manual. I built a DVA adapter to use along with my Fluke multimeter (I'm a EE) so I'm good on that front also.

As far as the one I bought being bad, the first time I took the boat out it after installing it the engine ran great. So I'd say that (at least at that point in time) the timer base was OK. But . I realize electronic stuff does sometimes fail on it's own accord, but often there's a reason for it failing (like at work when we have a nearby lighting strike we'll expect to see a few equipment failures at some point during the next two months).

 

[boobie]

Re: Why does a timer base fail????

Did you check it out to make sure the timer base was bad again?

 

[daselbee]

Re: Why does a timer base fail????

Metric, ....there are diodes in the timer base. They are of a type that requires a high bias current to forward bias them. The modern digital meters do not do the job, unless you use the diode test function of the meter. Using the diode test function only provides you a go-no go result at best. Testing the resistance of a timer base is sometimes futile using the newer meters.

Here is a cool thing though. Measure the output of the timer base with the DVA meter. It has to be a good DVA meter though. It cannot be the type that has been shown on this forum as a build your own DVA adapter. You can set the DVA meter on the 1 volt or .5 volt scale, and crank the engine. Not running, just cranking. If the timer base is good, and if the meter is sensitive, the meter needle will pulse every time the timer base outputs. So, measuring your particular base, the blue wire triggers # 1 on the stbd side, #2 on the port side; the purple wire triggers #3 stbd, #4 port; and the green wire triggers #5 on stbd and #6 on port. The white and black/white provide power FROM the pack TO the TB and back to the pack for ground return.

What would be even better is to put a scope on it. I sure would like to see the output waveform of some of these circuits.

Anyway, if it is bad, you will see erratic pulsing or no pulsing when measuring those wires. You can absolutely verify operation, in a manner that is not described in the book.

 

[metriccrescentwrench]

Re: Why does a timer base fail????

Update - pinched wire. :facepalm: One wire from the port side charge coil was pinched against a mounting stud. (Man there's a lot of wires crammed into a very small space !)

 

[blimp]

Re: Why does a timer base fail????

Do you think your old timer base could still be good?? Might be worth a swap and sell one if it was expensive...

You may have just unpinched that wire a bit during installation of the new one.

 

[metriccrescentwrench]

Re: Why does a timer base fail????

Do you think your old timer base could still be good?? Might be worth a swap and sell one if it was expensive...

You may have just unpinched that wire a bit during installation of the new one.

No, the old one was bad, no doubt about it.